ME Online Exclusive
Mining at the lowest cost per ton:
Innovations for large shovels
by William Gleason, Senior Editor
A Cat 7495 electric
rope shovel has
been in testing
at Caterpillar’s
proving grounds in
Arizona.
2
DECEMBER 2013 W
ith its 2011 acquisition of rival equipment
company
Bucyrus
International,
Caterpillar added underground mining and
large shovels to its line of products and further
solidified its standing as the leading mining
equipment manufacturer in the world with
solutions for every aspect of mining.
When Caterpillar spent $8.8 billion to
acquire Bucyrus, the global mining business
was flourishing, as mining companies around
the world worked to keep up with demands for
nearly every commodity. Flash forward to 2013,
and the global mining landscape looks very
different.
Lower demand for raw material from China
and India and falling commodity prices have
Mınıng engıneerıng
forced most mining companies to pull back on
their production.
The reductions from the mining industry
have hit equipment makers like Caterpillar and
Komatsu hard. In October, Caterpillar reported
that its quarterly earnings had fallen 44 percent.
The changing conditions have also changed
the narrative from Caterpillar and other
equipment makers to customers from offering
solutions to move the most tons per hour, to now
offering solutions for the lowest cost per ton.
In September, Caterpillar hosted some of
its mining customers and the trade press at
its Tinaja Hills Demonstration and Learning
Center near Tucson, AZ to talk about its range
of products, from its MineStar System designed
to help increase efficiency through better
equipment management and planning, all the
way up to the massive Cat 7495 and 7495HF
electric rope shovel lines acquired through the
Bucyrus takeover.
During the two days of presentations, the
recurring theme was more efficient operations
with a lower cost per ton and how to achieve this
goal. Experts spoke about improving haul roads,
cycle times, optimized payloads, improved fuel
consumption and mechanical maintenance.
One of the ways that Caterpillar plans to
help its customers in the near future is with the
Cat Power Demand Management System on
the Cat 7495 and 7495 HF electric rope shovel.
In short, the system generates and stores power
during swing deceleration and bucket lowering.
The system can then draw on that power when
needed.
While not yet commercially available, the
system that will permit mining companies to
power the shovels on just 4 MW of power has
been tested and validated as an off-grid solution
at Caterpillar’s Tinaja Hills proving grounds.
After field trials at an operating mine, it is
expected to be commercially available in 2014.
The standard practice for large rope shovels
uses multiple generators with a total of 8 MW
or more capacity to achieve rapid response when
peak power is required. Of course, multiple
generators increase maintenance and fuel costs.
Additionally, generator-powered electric rope
shovels require additional systems to dissipate
regenerated energy, because they cannot feed
electricity back into the power grid.
The Cat Power Demand Management System
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stores regenerative energy created
during swing deceleration and bucket
lowering, and the system uses that
power during periods of high demand
to reduce the generator load cycle.
Ultra capacitors enable the system to
store and release energy quickly. The
system enables a 4-MW generator to
handle a large electric rope shovel,
and it reduces fuel consumption by
employing regenerative energy.
The power demand management
system employs two methods of power
management: peak shaving and ramp
rate limiting. Peak shaving uses stored
energy to reduce the peak demand seen
by the power supply. The ramp rate
limiter is a similar concept, but instead
of reducing the peaks, it reduces the
rate at which power is demanded.
A 7495 shovel can switch from
regenerating 2.5 MW of power to
demanding 3.7 MW of power in less than a second.
This is a very difficult ramp rate for a generator to
supply. The system uses the energy stored in the
ultra-capacitors to allow the generators to ramp
up more slowly while still supplying all of the
necessary power to the machine. Likewise, when
power demand of the machine decreases quickly,
the generators ramp down slowly and the excess
energy recharges the ultra capacitors.
The Cat Power Demand Management System
in testing uses a skid with two 2-MW gensets
and associated hardware, and the energy storage
components are mounted on the roof of the
shovel. The system will be available as a retrofit
for 7495s.
Caterpillar also displayed its new dynamic
hoist brake with optional Smart Controller for
Cat 7495 and 7495HF electric rope shovels. The
dynamic hoist brake is designed to stop the dipper
from dropping during an uncontrolled event such
as a power drop or an emergency stop. The new
brake is designed to perform and survive a full
speed dynamic brake event with a fully loaded
dipper and, as a result, to minimize the risk of an
uncontrolled dipper drop.
The dynamic hoist brake is a drop-in
replacement for the standard hoist brake, which
was designed to be applied when the hoist
motor was not rotating. The new brake offers a
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number of advantages including friction material
that eliminates burnishing requirements and
reduces variations in brake torque, increased
thermal capacity, increased life, mechanical wear
indication and simplified, on-machine rebuild
procedures.
“The heavy-duty dynamic brake has
undergone a rigorous design, development and
validation process,” said Jim Ryan, new product
introduction program lead, electric rope shovels.
“We started with full bench testing to simulate
the application, and we’ve proven its performance
on our 7495 working at the Arizona Proving
Grounds.”
Caterpillar also has developed a smart
controller, available as an option, to continuously
monitor the applied torque, energy input and
wear of the dynamic hoist brake. The controller
also includes hardware that will apply additional
brake torque, if necessary, by a secondary
pneumatic piston.
The smart controller helps ensure that
brake torque levels do not drop below specified
levels even as a result of temperature extremes,
improper maintenance or other abnormalities.
The system also monitors brake energy levels to
anticipate thermal overload. It is easily fitted to all
7495 and 7495HF shovels using the Cat dynamic
hoist brake. n
Mınıng engıneerıng A Cat 7495 electric
shovel loads a haul
truck.
DECEMBER 2013
3